Electric arc gas heater

ABSTRACT

An electric arc gas heater having a housing provided with a chamber, an expansion nozzle and a constricted throat interconnecting the chamber and the expansion nozzle. A hollow upstream electrode opens into the chamber in rearwardly spaced relation to the throat and a portion of the expansion nozzle wall serves as the downstream electrode so that an arc passes completely through the throat.

United States Patent [72] inventors James H. Painter Winfield; Ronald J. Ehmsen, Bridgeton, both of, Mo. [211 App]. No. 802,980 [22] Filed Feb. 27,1969 [45] Patented June 29, 1971 [73] Assignee McDonnell Douglas Corporation St. Louis, Mo.

[541 ELECTRIC ARC GAS HEATER 11 Claims, 3 Drawing Figs.

52 user 219/383, l3/9,263/l9 5 11 lnt.Cl H05b7/18 [50] Field oiSearch .i 219/383- Primary Examiner- Volodymyr Y. Mayewsky AtlorneyGravely, Lieder & Woodruff ABSTRACT: An electric arc gas heater having a housing provided with a chamber, an expansion nozzle and a constricted throat interconnecting the chamber andthe expansion nozzle. A hollow upstream electrode opens into the chamber in rearwardly spaced relation to the throat and a portion of the expansion nozzle wall serves as the downstream electrode so that an arc passes completely through the throat.

ELECTRIC ARC GAS HEATER This invention relates in general to heaters for gaseous substances, and more particularly to electric arc gas heaters.

With the advent of space exploration, it has become necessary to test materials and spacecraft components under conditions simulative of the conditions those materials or components will encounter during planetary entry. To this end, electric arc gas heaters have been developed for generating high enthalpy gas streams into which the materials or components, or scale models of the later, can be placed. These are heaters follow the general construction for supersonic wind tunnels, having a constricted throat where sonic flow is achieved and an outwardly flared mount or expansion nozzle wherein the velocity of the airstream accelerates to supersonic levels.

While electric arcs have heretofore been used to elevate airstreams to higher enthalpy levels, it has been the practice to either establish the are between the expansion nozzle and a buttonlike cathode disposed immediately to the rear of the constricted throat or between the walls of the two tandem hollow electrodes extending axially rearwardly from the expansion nozzle. In the former case, the length of the arc remains more or less fixed, whereas in the latter case, the length of the arc is free to and does in fact vary, its length being dependent on several conditions such as the pressure and turbulence of the gas at the electrodes and the strength of the magnetic fields, if any, in which the electrodes are disposed.

ln arc gas heaters employed the principle of the fixed arc length, the upstream electrode is normally a button, and since the arc concentrates at one point on the button, these electrodes erode rapidly. indeed, when a gas such as air, which contains an oxidizing component, is passed through such heaters the button electrode must be surrounded with an inert gaseous shield. This, of course, is inconvenient and, much worse, involves the introduction of a foreign gas species into the airstream.

On the other hand, when natural arc lengths are utilized by employing hollow electrodes, the termini of the are continually pass around and axially along the cylindrical inner surfaces of the electrodes and thereby are not concentrated sufficiently at any one point to produce appreciable erosion. The downstream terminus of the arc is within the forward electrode upstream of the throat constriction on the device and, accordingly, the gasv is heated only for a limited distance within that electrode. Beyond the downstream terminus of the arc, the gas is cooled by the relatively cool walls of the electrode and nozzle and through the effects of expansion through the nozzle. Consequently, very high enthalpy levels cannot be obtained with natural arc length heaters.

Furthermore, arc-over is a problem with either of the foregoing existing heaters, and as a result arcs of extended lengths cannot be maintained. This, of course, imposes a severe limitation on the heating capabilities of such devices.

One of the principal objects of the present invention is to provide a gas heater for raising the enthalpy of gases passing through it to extremely high levels at the highest possible pressure. Another object is to provide an electric arc gas heater in which the arc does not appreciably erode the electrodes between which it is maintained. A further object is to provide a gas heater which does not require an inert gas shield around either of its electrodes. An additional object is to provide a gas heater which is simple in construction and economical to maintain. Still another object is to provide an electric arc gas heater capable of maintaining extremely long arcs without encountering arc-over. Another object is to provide an electric arc gas heater in which the length of the throat can be easily altered.

These and other objects and advantages will become apv parent hereinafter.

The present invention is embodied in an electric arc gas heater having a constrictor throat which opens into an expansion nozzle at its one end. The are is maintained through the entire throat between a downstream electrode in the expansion nozzle and a tubular upstream electrode disposed behind the opposite end of the throat.

The invention also consists in the parts and in the arrangements and combinations of parts hereinafter described and claimed. in the accompanying drawings which form part of the specification and wherein like numerals and letters refer to like parts wherever they occur:

FIG. 1 is a longitudinal sectional view of an electric arc gas heater constructed in accordance with and embodying the present invention;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1; and

FIG. 3 is a fragmentary sectional view taken along line 3-3 of FIG. 1.

Referring now in detail to the drawings, 2 designates an electric arc gas heater including a modular housing 4 formed from an end section 6, intermediate sections 8 and 10, and a nozzle expansion section 12, all of which are bolted rigidly together.

The end section 6 includes an end block 14 having a flanged constrictor sleeve 16 fitted into its one end. Also fitted into the same end of the block 14 between the flanges of the sleeve 16 is an annular insert 18, the exposed surfaces of which are located in spaced relation to the interior surfaces of the sleeve 16. The block 14 is relieved in the vicinity of the insert 18, and the cavity thereby formed communicates with the void between the sleeve 16 and insert 18 in the formation of a coolant channel 20. Opening into the channel 20 through the block 14 is a coolant inlet port 22 and a coolant outlet port 23. Outwardly from the downstream flange of the constrictor sleeve 16 the block 14 is cut inwardly in the formation of an annular gas injector channel 24 which is supplied through a radial duct 25 in the block 14. Beyond the opposite flange of the sleeve l6 the end block 14 is provided with a diametrally enlarged chamber 26, and fitted into the chamber 26 from the opposite end of block 14 is a primary gas injector ring 28 having a plurality of ports 30 arranged in two or more axially spaced rows with the ports 30 of one row being circumferentially offset with respect to the ports 30 in the other rows. The ports 30 further extend more or less tangentially with respect to the inner cylindrical surface of the ring 28 so that the gas discharging therefrom generates a vortex within the chamber 26 for the purpose of arc stabilization, rotation, and positioning. In surrounding relation to the ports 30 the block 14 is relived slightly and opening into this relieved portion is a gas inlet port 32. The injector ring 28 is held in place by means of an inwardly flanged nut 33 threaded onto the opposite end of the block 14. Fitted into the injector ring 28 is a sleevelike insulator 34 formed from a high dielectric substance capable of withstanding elevated temperatures such as hydrous aluminum silicate sold by the American Lava Corp., a subsidiary of the 3m Company, under the trademark LAVA. The annular insulator 34 supports an electrode enclosure 36 which projects outwardly therefrom and is provided with a coolant channel 38 into which coolant inlet ports 40 and a coolant outlet port 42 open. The electrode enclosure 36 receives and completely contains a tubular electrode 44 which extends axially rearwardly from and has its mouth disposed immediately to the rear of the constrictor sleeve 16. The electrode 44 is preferably formed from a suitable copper alloy such as one composed of percent silver and 20 percent copper.

The intermediate section 8 includes a block 46 which is secured to the end block 14 by means of bolts 48. The blocks 14 and 46 are electrically isolated from one another by an annular insulator plate 50 interposed between them and by tubular insulator elements 52 which completely sheath the bolts 48 within the block 46. The insulator plate 50 is formed from a suitable high-temperature dielectric material such as boron nitride, and contains slits 53 which extend between the annular gas injector cavity 24 and the inner periphery 50a of the insulator plate 50 (HO. 3). The slits 53 open generally tangentially into the interior of the sleeve 16 and extend in the same direction as the ports 30. Fitted within the block 46 is a former of which aligns with arid forms a continuation of the constrictor sleeve 16 within the end block 14. The block 46 is relieved beyond portions of the insert 56 and the insert 56 is disposed in outwardly spaced relation to the constrictor sleeve 54 so as to form an annular coolant channel 58 within the voids so defined. The channel 58 is supplied by an inlet port 60 and discharged through an outlet port 62, both of which communicate with the relieved portion thereof through the block 46. Outwardly from the leading or downstream flanges on the constrictor sleeve 54, the block 46 is cut inwardly from its end face in the provision of an annular injector cavity 64 which is supplied through a radial duct 66 formed in the block 46 The intermediate section 10 is identical to the intermediate section 8 and is bolted to the intermediate section 8 in the same manner as is the intermediate section 8 bolted to the end section 6. It will, therefore, not be described in further detail. The intermediate sections 8 and lare electrically isolated from each other by a high-temperature insulator plate 68 interposed between the blocks 46 of the two sections, and that insulator plate 68 contains slits 68' extending from the annular injector cavities 64 of the section 8 to the inner periphery 68a of. the insulator plate 68. The slits 68' are tangential to the sleeve 54 in the same direction as the ports 30. Additional intermediate sections such as sections 8 and may be provided, two being shown merely for convenience of illustration.

The constrictor sleeve 16 of the end section 6 and the constrictor sleeves 54 of the intermediate sections 8 and 10 axially align with one another and in combination form a constricted throat 69 within the housing 4. The nozzle expansion section 12 includes an inner block 70 and an outer block 72, the former of which is secured to the block 46 of the last intermediate section 10 by means of bolts 74 which are sheathed by tubular insulator elements 76. The electrical isolation of the inner block 70 is completed by an annular insulator plate 78 interposed between it and the block 46 of the intermediate section 10, and that plate 78 contains slits 79 extending from the annular cavity 64 of the section 10 to the inner periphery 78a of the insulator plate 78. Like the slits 53 and 68 the slits 79 are tangential to the sleeve 54 and extend in the same direction as the ports 30 so that the gas introduced through them enters the throat 69 in a swirl. The inner block 70 is further fitted with an inner expansion nozzle segment 80 which is tapered outwardly and flanged at its ends where it is pressed into engagement with the block 70. lntermediate the flanges of the nozzle segment 80 the inner block 70 is fitted with a tapered insert 82 which surrounds the center portion of the nozzle 80 in outwardly spaced relation thereto, and on each side of the insert 82 the block 70 is relived slightly. The voids thereby formed define a coolant channel 84 which is supplied through an inlet port 86 and discharged through another port (not shown).

The outer block 72 is very similar to the inner block 70 and likewise is fitted with a tapered insert 88 surrounded, in part,

by a coolant channel 90 which is supplied through an inlet port 92 and discharged through an outlet port 94. The outer block 72 is further fitted with an outwardly tapered outer expansion nozzle segment 96 which is likewise flanged at its ends for engagement with the block 72. The nozzle segment 96 forms a continuation of the inner nozzle segment 80 and the two in combination comprise a contoured expansion nozzle 98. Similarly, the outer block 72 is secured to the inner block 70 by means of bolts 99 which are sheathed in high-temperature tubular insulator elements 100, and interposed between the blocks 70 and 72 is an insulator plate 102 which extends inwardly to and is flush with the tapered inner surface of the expansion nozzle 98.

While the material from which inner expansion nozzle segment 8 0 is fabricated must be capable of withstanding high heating rates without deforming, eroding, or'decomposing, its composition is not otherwise critical. The outer expansion nozzle segment 96, however, serves as an electrode and, thereflanged constrictor sleeve 54 tind a sleevelike insert 56, the

fore, must not only be capable of withstanding high heating loys such as one composed of 80 percent silver and 20 percent copper have been found suitable for this purpose as well as pure OFHC copper which is marketed by the American Metal. Climax 101 of New York City, N. Y.

Disposed around the mouth section 12 in the vicinity of the insulator plate 102 is a magnetic field coil 104, and similarly disposed around the electrode enclosure 36 is another field coil 106. Both are used to position the arc terminations.

The housing 4 is mounted on a rigid support (not shown), and the coolant inlet ports 22, 40, 60, 86, and 92 are connected to a coolant source such as a supply of water by means of plastic or some other dielectric piping. The coolant outlet ports 23, 42, 62, and 94 are similarly connected to dielectric piping for carrying the coolant away from housing 4. The gas inlet port 32 and ducts 25 of the end sections, as well as the ducts 66 of the intermediate sections, are connected through suitable valving and piping to a source of compressed gas which in most instances will be air. The piping, of course, should be formed from a dielectric substance, at least in part, so that the sections 6, 8, and 10 remain electrically isolated from one another. Also, both coils 104 and 106 are connected through variable resistances to a separate source of direct current. Finally, electrical conduits are attached to the electrode enclosure 36 and outer block 72 of the mouth section 12 so that the tubular electrode 44 and the outer expansion nozzle segment 96 can be connected across an electrical energy source capable of supplying direct current.

ln operation, the object or specimen to be tested is placed beyond the end of the mouth section 12 in a duct or some other structure extending from the expansion nozzle 98. With 44 and outer nozzle segment 96 are placed at different potentials and in most cases the tubular electrode 44 will be the anode, although the device will function with the opposite polarity. The vacuum within the housing 4 facilitates the initiation of an arc between the outer nozzle segment 96 and the inwardly presented surface of the tubular electrode 44 as the potential difference between the two is increased, the arc being completely contained within the chamber 26, the constrictor throat 69, and the expansion nozzle 98. Once the arc is initiated pressurized gas is supplied to the gas inlet port 32 of the end section 6, and this gas enters the enlarged chamber 26 through the ports 30 in the gas injector ring 28. Since the ports 30 extend tangential to the inner surface of the ring 28, a vortex will be generated within the chamber 26, and this vortex will create a radial pressure gradient within the tubular electrode 44. By reason of this radial pressure gradient, the upstream terminus of the arc is shifted rearwardly into the tubular electrode 44 and, indeed, the exact position of the arc terminus is dependent, at least in part, on the extent of the vortex within the chamber 26 and the electrode 44. The gas, of course, escapes from the chamber 26 through the constricted throat 69. The flow through the throat 69 will achieve a sonic velocity, and only after the gas exits into the inner expansion nozzle segment is it accelerated to supersonic velocities. in any event, the arc passes through that portion of the gas stream contained within the chamber 26, the throat 69, and the inner expansion nozzle segment 80. Accordingly, the arc is in contact with the gas stream for an extremely long distance and by reason of this fact the gas stream is heated to extremely high enthalpy levels by the time it is discharged against the test specimen. Indeed, only for a short distance within the outer nozzle segment 96 is the gas stream not heated by the arc. The vortex further causes a relatively gradual mixing of the cold air with the arc, and thereby greatly reduces the tendency to extinguish the arc. The swirl generated by the vortex in the chamber 26 extends downstream into the throat 69 where it I from the end section 6 and nozzle 12 by insulator plates 50 and 78, and further by reason of the fact that the inner block 70 of the expansion nozzle 12 is insulated from the outer block 72 by the insulator plate 102, each of the sections 8, 10, 6, and 12 will assume a potential near that of the arc passing along their centerlines and thereby reduce the tendency of the arc to terminate prematurely at the sections 8 or 10 and cause an arc-over at the remainingdownstream insulator plates 68, 78, or 102, whatever the case may be. When arcover occurs the are current is conducted through the remaining sections 8, 10 and 12 to the downstream electrode 96, resulting in no further heating of the gas.

The potential difference between the electrode 44 and the outer nozzle segment 96 can be elevated still further without arc-over by injecting relatively small amounts of thesame gas into the ducts and 66 of the end section 6 and intermediate sections 8 and 10, respectively. This gas, of course, flows through the tangential slits 53, 6 8 and 79 and joins the main gas stream in the throat 69, maintaining the swirl or vortex originally induced by the primary gas flow through the ports of the ring 28. This in efiect encases the arc in an insulative sheath of cool air and maintains it centered in the throat 69. Stated differently, the cool air of the swirl passes along the walls of the sleeves 54 and inasmuch as it is cooler than the arc and thereby has a higher resistance it serves an an insulator, preventing arc-over to the sleeves 54. Thus, larger arc lengths can be maintained and more power is dissipated in the gas passing through the throat 69 and expansion nozzle 98. This, in turn, elevates the enthalpy of the gas stream to even higher values.

Since neither terminus of the arc is concentrated at a specific point for a significant time but on the contrary is free to shift over a relatively large area, the effects of arc erosion and stream contamination also are reduced to a minimum. In this connection, the upstream terminus of the arc is free to shift both circumferentially and axially on the inner cylindrical surface of the tubular electrode 44, its exact position at any given instance being dependent on the gas momentum flux as well as the strength of the radial component of the magnetic field surrounding the electrode 44. The latter can be varied by both shifting the field coil 106 axially on the electrode enclosure 36 and by varying the current passing through it. The coil 106 further serves to rotate the upstream terminus of the are around the inner surface of the tubular electrode 44. It is, therefore, not necessary to employ an inert gas shield to protect the upstream electrode against the resultant erosion caused by oxidation. The downstream terminus of the arc is rotated around the conical surface of the nozzle segment 96 by the coil 104 and can be axially positioned by varying the field current or by axially shifting the coil 104 itself.

The modular construction of the gas heater 2 enables the operator to readily alter the construction of the heater 2 to suit the particular test he desires to perform. For example, if an extremely long arc is desired, additional intermediate sections 8 or 10 may be interposed. 0n the other hand, if a shorter arc is sufficient or if arc-over becomes a problem, either intermediate section 10 or 8 may be removed, and this will shorten the arc length and thereby decrease the arc gas contact length so as to alleviate the arc-over problem. The intermediate sections 8 and 10, of course, need not have the same axial dimension.

This invention is intended to cover all changes and modifications of the example of the invention herein chosen for purposes of the disclosure which do not constitute departures from the spirit and scope of the invention.

What we claim is:

l. A heater for raising gas streams to extremely high energy levels, said heater comprising a housing having a chamber, an

outwardly flared expansion nozzle, and a constricted throat interconnectmg the nozzle and chamber, the housing further having a gas inlet port in communication with the chamber for supplying pressurized gas to the chamber, a downstream electrode in the expansion nozzle, and an upstream electrode carried by the housing and being a hollow member which opens into the chamber in rearwardly spaced relation to the throat, whereby when the first and second electrodes are placed at different potentials an arc will pass through the throat between the electrodes.

2. A heater according to claim 1 wherein the expansion nozzle comprises outwardly flared walls and the first electrode is in those outwardly flared walls.

3. A heater according to claim 2 and further characterized by injector means for injecting pressurized gas into the throat between the chamber and the expansion nozzle.

4. A heater according to claim 2 wherein the gas inlet ports communicate with the chamber substantially tangential to the walls defining the chamber, whereby a variable strength vortex is generated within the chamber and throat for maintaining the upstream terminus of the are within the hollow portion of the upstream electrode and for the purpose of gradually mixing the cold air with the arc, thereby maintaining an arc throughout the length of the constrictor.

5. A heater according to claim 2 wherein the housing includes an intermediate section which contains a portion of the throat and is removable so that the length of the throat and the arc can be altered.

6. A heater according to claim 4 wherein the expansion nozzle comprises inner and outer nozzle segments which form a substantially continuous outwardly tapered surface extending from the end of the throat, the nozzle segments being electrically isolated from one another and the outer nozzle segment carrying the downstream electrode.

7. A heater according to claim 6 wherein the tapered surface of the outer nozzle segment is fonned from a substance capable of conducting an electric current whereby the substance forms the downstream electrode.

8. A heater according to claim 7 and further characterized by means for passing a magnetic field through the downstream electrode for the purpose of positioning the arc termination.

9. A heater according to claim 4 and further characterized by means for passing a magnetic field through the upstream electrode for the purpose of positioning the arc termination.

10. A heater according to claim 4 wherein the housing comprises an end section in which the chamber is located, at least one intermediate section in which at least a portion of the throat is located, and a nozzle expansion section in which at least a portion of the expansion nozzle is located, and wherein electrical insulators are interposed between the sections for electrically isolating the sections one from another.

11. A heater according to claim 3 wherein the injector means introduces the gas generally tangentially into the throat so as to form a swirl therein, the swirl being in the same direction as the vortex in the chamber.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 590 Z19 Dated June 29, 1971 James H. Painter et a1. Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 14, "mount" should read mouth line 30,- "employed" should read employing Column 4, line 6, "Metal Climax 101" should read Metal Climax Corp.

after column 6, insert Reference Cited UNITED STATES PATENTS l ,l28 ,640 2/1915 Wilmowsky 219-383 2 ,403,163 7/1946 Ziegler 219-383 3, 029 ,635 4/1962 Fetz -2l9-l21X 3,371,189 2/1968 Kemeny et a1. 219-383 3 ,461 ,190 8/1969 Kemeny et a1 "263-52 Signed and sealed this 20th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-IOSO (10-693 UscoMM-Dc a0 75.p5

a as sovzurmnn' Pmmms ornc: 1969 o-sss-su 

1. A heater for raising gas streams to extremely high energy levels, said heater comprising a housing having a chamber, an outwardly flared expansion nozzle, and a constricted throat interconnecting the nozzle and chamber, the housing further having a gas inlet port in communication with the chamber for supplying pressurized gas to the chamber, a downstream electrode in the expansion nozzle, and an upstream electrode carried by the housing and being a hollow member which opens into the chamber in rearwardly spaced relation to the throat, whereby when the first and second electrodes are placed at different potentials an arc will pass through the throat between the electrodes.
 2. A heater according to claim 1 wherein the expansion nozzle comprises outwardly flared walls and the first electrode is in those outwardly flared walls.
 3. A heater according to claim 2 and further characterized by injector means for injecting pressurized gas into the throat between the chamber and the expansion nozzle.
 4. A heater according to claim 2 wherein the gas inlet ports communicate with the chamber substantially tangential to the walls defining the chamber, whereby a variable strength vortex is generated within the chamber and throat for maintaining the upstream terminus of the arc within the hollow portion of the upstream electrode and for the purpose of gradually mixing the cold air with the arc, thereby maintaining an arc throughout the length of the constrictor.
 5. A heater according to claim 2 wherein the housing includes an intermediate section which contains a portion of the throat and is removable so that the length of the throat and the arc can be altered.
 6. A heater according to claim 4 wherein the expansion nozzle comprises inner and outer nozzle segments which form a substantially continuous outwardly tapeRed surface extending from the end of the throat, the nozzle segments being electrically isolated from one another and the outer nozzle segment carrying the downstream electrode.
 7. A heater according to claim 6 wherein the tapered surface of the outer nozzle segment is formed from a substance capable of conducting an electric current whereby the substance forms the downstream electrode.
 8. A heater according to claim 7 and further characterized by means for passing a magnetic field through the downstream electrode for the purpose of positioning the arc termination.
 9. A heater according to claim 4 and further characterized by means for passing a magnetic field through the upstream electrode for the purpose of positioning the arc termination.
 10. A heater according to claim 4 wherein the housing comprises an end section in which the chamber is located, at least one intermediate section in which at least a portion of the throat is located, and a nozzle expansion section in which at least a portion of the expansion nozzle is located, and wherein electrical insulators are interposed between the sections for electrically isolating the sections one from another.
 11. A heater according to claim 3 wherein the injector means introduces the gas generally tangentially into the throat so as to form a swirl therein, the swirl being in the same direction as the vortex in the chamber. 